When metal-organic chemical vapor deposition (MOCVD) is used as the epitaxy technique to grow an epitaxial layer (e.g., InGaAs) on a substrate with patterned windows of silicon dioxide or silicon nitride, the local growth rate on the substrate is enhanced. This is generally referred to as Selective Area Epitaxy (SAE). The reason for the enhancement is due to the fact that growth on top of the oxide or nitride region is inhibited. Thus, the extra material (e.g., tri-ethyl-Gallium and tri-methyl-Indium) migrate towards the uncovered region, enhancing the local growth rate. The enhancement factor depends on the ratio of oxide (nitride) area to the available growth area and the diffusion coefficient of the metal-organic sources.
Previous applications of SAE have all been towards edge emitting lasers and integrated optoelectronic devices. For example, in U.S. Pat. No. 5,659,640 issued to Joyner the inventor teaches the use of SAE for making an integrated waveguide with an optical grating. Suitable mask geometry is chosen to ensure that the deposition process produces the desired optical structure, i.e., an optical grating or even a stack of Quantum Well regions (QWs). In U.S. Pat. No. 5,418,183 Joyner et al. teach the use of SAE for producing a reflective digitally tunable laser. Another type of multiple QW distributed feedback semiconductor laser grown with the aid of SAE is taught by Shim et al. in U.S. Pat. No. 5,614,436. Additional references illustrating the use of SAE for simultaneously growing optical devices in the same plane are found in the articles of Joyner et al., "Extremely Large Band Gap Shifts for MQW Structures by Selective Epitaxy on SiO.sub.2 Masked Substrates," IEEE Phot. Tech. Lett., Vol. 4, No. 9 (September 1992), pp. 1006-9 and Caneau et al., "Selective Organometallic Vapor Phase Epitaxy of Ga and In Compounds: A Comparison of TMIn and TEGa versus TMIn and TMGa," J. Crystal Growth, Vol. 132 (1993), pp. 364-370.
These and similar prior art devices typically have InGaAs QWs in their active region. These QWs are regrown on a patterned substrate with different openings between two oxide strips. The thickness of the QW is inversely proportional to the oxide strip opening due to SAE. Moreover, since the SAE enhancement factor for In is more than the Ga enhancement factor, the In content of the QW is also a function of the oxide strip opening. Hence, the emission wavelength of each laser in the array can be tailored by the oxide strip opening.
The optical elements of the prior art devices are all located in the plane in which SAE is performed. In other words, SAE is performed on a surface which provides for planar alignment between the optical elements. Hence, the resulting devices are limited to a planar element distribution as encountered, e.g., in edge emitting lasers.